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Negaprion brevirostris, lemon shark, is unusually social for a shark. When juvenile N. brevirostris were introduced to an empty two-compartment tank, they showed no preference for either side; however, when they were introduced to a tank in which one compartment was empty and the other had another lemon shark, the juvenile N. brevirostris spent more time in the company of the other shark than in the empty compartment (Guttridge et al., 2009).
Compared to the aggregation behavior observed in ragged-tooth sharks and bull sharks, there is no factor aside from the presence of the other sharks in the laboratory setting that might cause N. brevirostris to aggregate. Unlike other sharks, such as the basking shark, who are observed to be alone most of the time, N.brevirostris have been seen swimming in groups of two or more individuals most of the time (Gruber, Nelson,&Morrissey 1988)(Sims et al. 2000).
Also, interestingly enough, unlike the display interactions Le Beouf (2004)observed between eavesdropping salmon sharks, Lamna ditropis, no reports of aggressive encounters were noted in interactions between the lemon sharks in laboratory setting (Guttridge et al., 2009).
Not only are lemons sharks more socially responsive to other lemon sharks, they also interact with many other species of marine teleosts by swimming behind an organism and mimicking its movements (Papastamatious et al., 2006). In Guttridge’s experiment in 2009, N. brevirostris was observed interacting with a pair of nurse sharks in this way. Besides nurse sharks (Ginglymostoma cirratum), other common organisms N. brevirostris have been observed to interact with are schools of jacks (Caranx) and barracudas (Sphyraena barracuda), southern stingrays (Dasyatis americana), and under special conditions, slender suckerfish (Echeneis naucrates) (Papastamatious et al., 2006).
The size-specific grouping due to overlapping diets may not be the only reason why size segregation is practiced. Assuming that sharks do practice size segregation, this grouping behavior should increase the overall fitness of every participant (Conradt, 1998). Thus one plausible reason why sharks may benefit from forming size-specific groups may be that hunting efficiency and overall foraging success increase due to cooperative behavior between each of the members because of their similar levels of hunting experience (Guttridge et al, 2009). However, are the sharks really cooperating?
According to Klimley et al.’s observations in 2001, white sharks ( Carcharodon carcharias ) that gathered around a seal colony on Anõ Nuevo Island off the coast of California never interacted; sharks only approached one another after eavesdropping on a kill made by another shark (Le Beouf, 2004). Any attempts to steal food resulted in threatening displays of tail slaps and breaching – jumping out of the water – by the one who made the kill (Klimley et al ., 2001). These white sharks appear to have gathered in groups of similar size solely because of their shared prey: the seals (Le Beouf, 2004).
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